fix TypeError: nodes is not iterable when loading graph (#5660)

## Summary
- Fixes Sentry issue CLOUD-FRONTEND-STAGING-29 (TypeError: nodes is not
iterable)
- Adds defensive guard to check if nodes is valid array before iteration
- Gracefully handles malformed workflow data by skipping node processing

## Root Cause
The `collectMissingNodesAndModels` function in `src/scripts/app.ts:1135`
was attempting to iterate over `nodes` without checking if it was a
valid iterable, causing crashes when workflow data was malformed or
missing the nodes property.

## Fix
Added null/undefined/array validation before the for-loop:
```typescript
if (\!nodes || \!Array.isArray(nodes)) {
  console.warn('Workflow nodes data is missing or invalid, skipping node processing', { nodes, path })
  return
}
```

Fixes CLOUD-FRONTEND-STAGING-29

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5660-fix-TypeError-nodes-is-not-iterable-when-loading-graph-2736d73d365081cfb828d27e59a4811c)
by [Unito](https://www.unito.io)

src/scripts/app.ts

@@ -1121,6 +1121,13 @@ export class ComfyApp {
       nodes: ComfyWorkflowJSON['nodes'],
       path: string = ''
     ) => {
+      if (!Array.isArray(nodes)) {
+        console.warn(
+          'Workflow nodes data is missing or invalid, skipping node processing',
+          { nodes, path }
+        )
+        return
+      }
       for (let n of nodes) {
         // Patch T2IAdapterLoader to ControlNetLoader since they are the same node now
         if (n.type == 'T2IAdapterLoader') n.type = 'ControlNetLoader'